Fridge Freezer Thermostat - Adjustment Screws

[Martin]

I have a 20 year old Hotpoint RF60 2-door upright fridge freezer. The bottom half is the freezer and the top half is the fridge. There's only one compessor, and a single electro-mechanical thermostat in the fridge is the only temp control for the whole unit; it's sensor tube is attached to the rear of the heat exchanger in the fridge compartment.

Last week the thermostat packed up. I called a repair firm and they changed the thermostat. However, even on its warmest setting, the freezer is at -24C (at least - end of thermometer scale) and the fridge is colder than I would like - naturally, the compressor is running for much of the time but the unit does go through a cycle i.e there are times when the compressor is off and the heat exchanger in the fridge defrosts itself. However, something's not right. Yesterday, the firm replaced the new thermostat but the unit is still running too cold.

To try and understand how the thermostat works, I partly stripped the old defective one. The outer 2 contacts appear to be controlled by the bellows at the end of the sensor tube. However, there is a central contact which seems to be connected to one of the edge contacts at all times except when the thermostat is turned to Off. I don't understand what this central contact is for.

There are 2 factory preset screws which control spring tensions and I presume these screws control the temp at which the compressor contacts make and break. One's accessible on the top of the thermostat and the other's visible through a hole adjacent to the first screw. I'd be grateful for advice on how best to go about adjusting these so that with the user control knob in the middle of its scale, I have a freezer temp of around -18C and a correspondingly cool fridge.

I've tried phoning Hotpoint for help but there is no technical department. Any guidance and clarification would be much appreciated.

[PipeDown]

Those thermostats are generally not user adjustable (exept for the obvious knob).

They may have used a universal aftermarket part instead of a factory original. They may also have positioned the temp probe (wire like lead) inside the insulation (or otherwise in the wrong spot) causing it to run too cool.

Turn the other knob to "freezer colder" to close the vent and at least the fridge will warm up a bit even if the freezer is still too cold

[Martin]

Many thanks.

I'm sure you're right: they've used a universal thermostat instead of the original part - assuming it's available. Now, the compressor has been running for hours and the fridge is below zero. I watched him reconnect the sensor tube and I'm sure that was positioned correctly. The fellow thought it possible he'd reconnected the contacts wrongly, but as the fridge has gone though on-off cycles, I imagine he reconnected correctly, but he was unsure where the central contact leads to i.e. the contact that breaks when the thermostat is switched off. He thought it might be the light!

I've run some simple tests using the force required to make and break the contacts seeing what effect both the user control and the factory preset screws have. It appears that the user knob controls the point at which the contacts break i.e. when the compressor is switched off.

The screw accessible on the surface of the thermostat appears to affect the make and break force: clockwise increases both the make and the break forces. The screw inside the body appears to affect only the break force - clockwise lowers the force.

I need to sleep on this, and tomorrow I will have a go at adjusting the screw(s) and will report back in due course. This fridge freezer has no vent - there are heat exchangers in both the freezer and the fridge. There are no fans in either compartment and no visible physical connections between the 2 compartments.

In future, I don't buy any appliance unless I can get hold of the service manual. And the Hotpoint Indesit range is definitely out: they refuse to sell the manuals and have no facility for technical help - unlesss you call their own service personnel out.

I'll report the outcome for future reference.

Thanks again.

[PipeDown]

The universal nature of the replacement part probably required both a normally closed and a normally open contact to the switch. It might be used on a different fridge but apparently not yours.

Hmm, If you hooked up the wrong side of the switch, the compressor would run when it was too cold and stop if it were too warm. It would either run all the time or not at all.

When you figure it out, you will be the resident expert.

I never owned a freezer on the bottom model, maybe they are different than I expect.

To be fair, you did say it was 20 years old. There are still some things that are hard to find for free on the web, service manuals are one of them, shed plans are another.

A thermostat regulates temperature at the point where the sensor tube is mounted. Hang a thermometer at the same spot and see if this what you wanted. Moving it closer to the source of cold (coils) should cause warmer air as these are usually intended to sense the circulating air in the box not the thermal mass of a solid object. Try moving the sensor to a new location or if it is touching the wall, move it away.

[groucho78]

hi, I know this post was over 15 years ago , but I need some help, ? did you ever find out what the adjustment screws do? I know one is the cold range which is the tougher spring loaded screw, but the other is a differential between cold and warm temperature, which either cuts in later or sooner. That is what I think, If I adjust the differential screw anti clockwise the fridge side will be warmer, and the freezer stays at -18 celsius, but if turned further in causes fridge to stay on for longer and get colder. So my theory is the diff screw needs to find a balance between turning on too late and turning off too soon....I am increasing temp by control knob ech 24 hours which makes compressor kick back in.. mine is a ranco Vt9 thermostat . I believe differential should be somewhere between 16 and 24 turns out from being seated fully in.....I have tried at 14 turns and it gets too cold in freezer, but now its at the right temp in freezer but takes 45 hours to come back on after auto defrost... I will try adjusting cold range screw and do 1 turn out to msee if this helps fridge cut in sooner. but at the minute, my fridege only cuts back in at 10-12 degrees celsius. I am so close to normal running cycle.

[Paul]

Hi . Differential screw is the screw that is easiest to turn. This screw is how long the fridge stays off until it reaches a certain temp. Then it kicks compressor back on. This screw is factory set. So if you turn the range screw one way, then you do the opposite for for the diff screw. And vice versa. These are so sensitive. So I have the same problem. Fridge goes off but wont come back on after a long time. Here is my theory: range screw shold be about 6-7 turns out from fully seated . Did diff screw between 20-26. I would like to know if you worked it out and could you let me know how many turns out each screw is from being fully in. If you are getting around 3.5 degrees on mid point of control knob, you should be okay, then you will need to adjust the diff screw in. But your situation is slightly different. Range screw on yours could be way off. Alway start at 5 turns out for range and 23 for differential. All thermostats are not the same even ones that are branded the same are set up differently. I have had 2 thermostats of the same make from the same seller andscrews on both were set 3 or 4 turns either direction so one would be 7.5 turns and 28 turns out and the other was 9 turns and 32 turns out. Please let me know how yours is set up? Thanks